In a substrate processing apparatus such as a plasma processing apparatus, a substrate is processed with a gas supplied from a gas supply system into a processing vessel of the substrate processing apparatus. In the substrate processing apparatus, multiple kinds of processes may be performed in sequence. For the purpose, the gas supply system may be configured to control flow rates of one or more gases selected from multiple kinds of gases and supply the one or more gases into the processing vessel.
To elaborate, the gas supply system includes a multiple number of first lines, a multiple number of first valves, a multiple number of flow rate controllers, a multiple number of second lines, a multiple number of second valves, a third line and a third valve. The first lines are respectively connected to a plurality of gas sources. The first valves are respectively provided at the first lines. The flow rate controllers are respectively provided at the downstream sides of the first lines. The second lines are respectively provided at the downstream sides of the flow rate controllers. The second valves are respectively provided at the second lines. The third line is connected to the second lines. The third valve is provided at the third line. The third line is connected to the processing vessel at the downstream side thereof.
Each of the flow rate controllers may be implemented by a pressure type flow rate controller as described in Patent Documents 1 to 3. The flow rate controller of this type includes an orifice, a control valve, a first pressure gauge and a second pressure gauge. The control valve is provided at the upstream side of the orifice. The first pressure gauge is configured to measure an internal pressure of the line between the control valve and the orifice. The second pressure gauge is configured to measure an internal pressure of the line at the downstream side of the orifice. In this pressure type flow rate controller, the control valve is controlled according to a set flow rate. When a pressure measurement value of the first pressure gauge is equal to or larger than twice a pressure measurement value of the second pressure gauge, the control valve is controlled to reduce a difference between the set flow rate and an output flow rate calculated from the pressure measurement value of the first pressure gauge. Further, when the pressure measurement value of the first pressure gauge is smaller than twice the pressure measurement value of the second pressure gauge, the control valve is controlled to reduce a difference between the set flow rate and an output flow rate calculated from a difference between the pressure measurement value of the first pressure gauge and the pressure measurement value of the second pressure gauge.
Patent Document 1: Japanese Patent No. 3,291,161
Patent Document 2: Japanese Patent No. 4,102,564
Patent Document 3: Japanese Patent No. 4,866,682
A state of the gas supply system may be changed as an operating time of the substrate processing apparatus passes by. If the state of the gas supply system is changed from its previous state, the flow rate of the gas supplied into the processing vessel to process the current substrate may become different from the flow rate of the gas which is supplied into the processing vessel to process the previous substrate, though the gas is supplied into the processing vessel of the substrate processing apparatus according to the same process recipe. Accordingly, there may be caused a problem that the state of the substrate processed previously and the state of the substrate to be processed next are different. Thus, it is required to inspect the gas supply system.